After the discovery of the central nervous system stimulatory properties of 3-(1-methyl-2-phenylethyl)-N-(phenylcarbamoyl)sydnone imine (Sydnocarb; U.S.S.R. 329,890 and Offenlegungsschrift 2,028,880) various analogues have been reported. U.S.S.R. 222,370 and Offenlegungsschrift 2,738,022 disclose sydnone imines which contain phenyl, 1- or 2-phenylethyl and the phenylisopropyl groups in 3-position as well as N-meta- and para-chlorophenyl and N-phenyl carbamoyl groups. Variations of 3-benzyl sydnonimines are disclosed in U.S. Pat. No. 3,277,108. Other variously substituted 3-aralkyl sydnonimines are disclosed by Olovyanishinkiva et al. Khim. Geterotsikl Soedin, 2 170-175 (1978) and 9 1198-1203 (1975).
Sydnocarb is conventionally produced by cyanomethylation of amphetamine followed by nitrosation and ring closure with a mineral acid to yield sydnophen as an acid halide salt which is reacted with phenylisocyanate under mildly basic conditions to introduce the N-phenylcarbamoyl group. As an asymmetric compound, amphetamine may be employed as the initial reactant as the racemic d,l-mixture or as the pure d- or l-isomer to yield racemic or optically active sydnophen and ultimately sydnocarb.
Yashunskii et al., J. Med. Chem., 14 1013-1015 (1971) disclose the marked CNS-stimulatory effect of 3-(1-methyl-2-phenylethyl) sydnonimine (Sydnophen). The relative activities of a large number of alkyl, aryl and aralkylsydnonimines are presented in Table 1 on page 1014. Most of them, including compound XVIII (2-hydroxy-1-methyl-2-phenylethyl-sydnonimine), were essentially inactive central nervous system stimulants relative to compound XIII (Sydnophen), demonstrating the criticality of the structure of the 3-substituent in the Sydnocarb series of compounds as far as CNS stimulatory activity is concerned. Thus, although the activity profile of Sydnocarb is not identical to that of amphetamine, or for that matter Sydnophen, CNS stimulatory activity is a common property of the initial reactant amphetamine, the intermediate Sydnophen and the final product Sydnocarb.